Ion diffusion in a liquid usually could be treated as a movement of an ion cluster in a viscous media. The experimental results showed that chloride diffusion coefficient of concretes decreased not only with increasing. Dec 01, 2016 a phasefield model is proposed to describe cracking and its coupling with diffusion. The chloride penetration into the concrete was realised with a non steady state migration test and modelled with the finite element method cosmosffe thermal software. However, the long term methods are often not preferred in practice because they are. A phasefield model is proposed to describe cracking and its coupling with diffusion. Pdf nonsteady state chloride diffusion in concrete with. These tests include the rapid chloride penetrability test, astm c1202, the nonsteadystate migration experiment, nt build 492, and numerous other methods. Experimental and simulation study on diffusion behavior of. The present paper investigates the chloride binding of selfcompacting concrete with different crack lengths using non steady state migration test. However, a non steady state electrophoretic test, nt bilud 492 of nordtest, has been proposed.
Testing chloride penetration resistance of concrete. Nevertheless, in real concrete structures, multiple cracks instead of a single crack are most commonly observed. This test takes less time and is less complicated than the steady state electrophoretic. The chloride diffusivity in cracked zone is expressed as functions of crack width. In the work, the increasing diffusion coefficient from the total cracked. Lattice modeling of chloride diffusion in sound and cracked concrete.
While our specific interest is on diffusion of chloride ions in hardened cement paste, the proposed model has more general applicability to any porous material potentially developing cracks. The steadystate chloride diffusion coefficient was evaluated using the. Chloride migration coefficient from nonsteadystate migration experiments nt build 492 size. The present study investigates nonsteady state chloride diffusion in concrete. Effect of transverse crack on chloride penetration into. Determination of the concrete chloride diffusion coefficient. However the nonsteadystate, dns, is expressed by volume of concrete or mass of cement and therefore refers to the total amount of chlorides in the sample. Therefore, this study proposes a test method to evaluate the selfhealing capacity of cementbased materials in. Simulation of chloride diffusion in cracked concrete with. Sustainability 2017, 9, 282 3 of 14 sustainability 2017, 9, 282 3 of 14 figure 1. The development of nondestructive ultrasonic techniques is thus needed for. Chloride diffusion in three different position of aggregate after 20 weeks the halfcell potential values of each bar of the steel bars in each sample figure 4. The model is formulated in gurtins framework and first applied to a twodimensional. Nonsteady state chloride diffusion in concrete with different crack densities, materials and structures, vol.
Therefore, the aim of this study is to analyze the possibility of determination of the chloride diffusion coefficient in accelerated chloride migration test for various concretes and whether the applied blended. In section 4, individual test procedures are presented. Secondly, the influential zone caused by the crack is limited to a distance of 10 mm at both sides from the crack. In his study, mu, 20 adopted a nonsteady state diffusion test to investigate the relationship between the diffusion coefficient and crack density. Many researchers have also developed test methods to measure the chloride diffusion coefficient under steady state and nonsteady state conditions page 1981. The present paper adopts a nonsteady state diffu sion test to study the chloride transport in concrete samples with different crack densities prepared by the nondestructive notch method. Diffusion coefficient from nonsteady state condition is very vulnerable to crack width since it reflects the local chloride penetration depth in the crack width, so that the enlarged diffusion coefficient reaches to 160 times for normal condition park et al. Aacm concrete and conventional concrete specimens of similar strength, developed for structural applications, were exposed to a 5% nacl solution. Influence of cracks and crack width on penetration depth.
Prediction of chloride ion penetration of recycled. Microstructural refinements of concrete due to fiber. The gain in mass per unit area over the density of water is plotted versus the square root. Nonsteady state chloride diffusion in concrete with different crack.
Assuming a steadystate condition, the equivalent flux jt for the rev can be calculated using equation 3 based on the flux and the crosssectional area. Carbonation, freezethaw cycles, and chloride penetration of concrete are the important factors for reinforced concrete rc structures. Baroghelbounyinfluence of traversing crack on chloride diffusion into concrete. Testing chloride penetration resistance of concrete fhwa. Chloride migration coefficient from nonsteadystate migration experiments 38. Diffusion coefficient from non steady state condition is very vulnerable to crack width since it reflects the local chloride penetration depth in the crack width, so that the enlarged diffusion coefficient reaches to 160 times for normal condition park et al.
Chloride diffusion assessment in rc structures considering. These methods monitor the current passed through a sample submerged in a solution. The results showed that the proposed multiscale model gave a little higher chloride diffusivity of uhpc than experiment results. Measurement of the steady and nonsteadystate chloride. Time and crack effect on chloride diffusion for concrete with. Crack geometry characteristics, such as crack width, crack depth, crack shape parallel crack and tapered crack, and crack spacing, are considered. Concrete is not inert relative to the chlorides in the pore solution. Materials free fulltext using the steadystate chloride. The present study investigates nonsteady state chloride diffusion in concrete samples with different crack densities prepared by a nondestructive notch method.
The other method is the nordtest method nt build 492. Permeability plays an important role in governing the durability of concrete in deleterious environments. Advances in materials science and engineering 2018 article. Using the steadystate chloride migration test to evaluate. In this analysis the nonsteady state of the chloride diffusivity is considered. However the non steady state, dns, is expressed by volume of concrete or mass of cement and therefore refers to the total amount of chlorides in the sample. Azad impact on corrosion of reinforcement chloride. From the chloride penetration profiles on 117 concrete cores, the influence of the crack width, measured on the concrete surface exposed to chlorides, on the. Nonsteady state chloride diffusion in concrete with. Influence of traversing crack on chloride diffusion into concrete. Diffusion through liquids is considerably more rapid than diffusion in the solid state, so that processes of this kind can transport salts deep into the interior of, for example, concrete structures. In order to investigate chloride migration in cracked concrete, considering the mesoscopic heterogeneity of concrete, concrete modeled here is treated as a fourphase composite consisting aggregate, mortar, crack, and interfacial transition zone itz.
Nonsteady chloride diffusion tests were performed to validate the proposed model. These tests include the rapid chloride penetrability test, astm c1202, the non steady state migration experiment, nt build 492, and numerous other methods. The squared values represent the spectral energy densities of diffuse wave. Chloride diffusion in the steadystate condition through cracked concrete. So, it is meaningful to study the influence of crack depths on chloride transport in cracked selfcompacting concrete. Usually, the socalled steady state diffusion coefficient, ds, refers to the pore solution concentration and therefore expresses the movement of water soluble chlorides. This test method assesses the coefficient of chloride migration, which is a measure of the resistance of the tested material to chloride penetration. Using experimental results of chloride penetration depth, the apparent chloride diffusion coefficient of sound concrete is calibrated as 3. Ma 5 the influence of different preparation methods on the aggregation status. However the nonsteady state, dns, is expressed by volume of concrete or mass of cement and therefore refers to the total amount of chlorides in the sample. Any cracks or other imperfections on the surface open up additional routes for. The precise calculation of steady state chloride diffusion coefficients is laborious, expensive, and time consuming due to the fact that it is necessary to take liquid samples for the chlorides to be analysed.
Salt ponding 2 and bulk diffusion 3 are examples of non steady state chloride diffusion tests where the apparent diffusion coefficient is determined by fitting profiles of the acid soluble chloride concentration to ficks second law of diffusion 4. Park, kwon, and jung 2012 evaluated the crack effect on chloride diffusion in splitting cylinder concrete by nonsteadystate migration test and proposed an analytical. The different mechanisms of chloride penetration are presented. The cracked zone and sound zone of concrete are given individual diffusion coefficients. The contour of free chloride concentration and chloride penetration depth at 8 weeks and 20 weeks. The influence of basic properties of concrete on its chloride penetrability is also discussed. Bound chloride ingress in alkali activated concrete. The model is formulated in gurtins framework and first applied to a twodimensional plate subject to mechanical and. Other crack characteristics, such as chloride depth, crack shape equalwidth crack or tapered crack, crack density, and spacing, are not studied in detail.
The durability of the studied compositions was evaluated by the absorption of water into concrete under capillary and under immersion action, the non steady state chloride migration tests and fourpoint electrode resistivity measurements. Interest in selfhealingcrack technologies for cementbased materials has been growing, but research into such materials remains in the early stage of development and standardized methods for evaluating healing capacity have not yet been established. The present study investigates nonsteady state chloride diffusion in concrete samples with different crack densities prepared by a. Cracks provide diffusion path for chloride ions transport from the external environment into the concrete, resulting in the durability degradation of concrete structures. The relationship between diffusion coefficient and crack density is discussed.
Therefore, this study proposes a test method to evaluate the selfhealing capacity of cementbased materials in terms of their resistance to. The timedependent chloride diffusion model was established based on the. Many different conditions of cracks may occur in concrete structures under. Simple technique for tracking chloride penetration in concrete. Pdf nonsteady state chloride migration and binding in. In this paper, the concentration of chlorides is monitored by measuring the conductivity of the anolyte which initially is distilled water. Chloride penetration resistance properties of concrete. In this thesis, microstructural refinement and corrosion resistivity performance of fiber reinforced concrete frc were. The precise calculation of steadystate chloride diffusion coefficients is laborious, expensive, and time consuming due to the fact that it is necessary to take liquid samples for the chlorides to be analysed. Calculation of the rate of coagulation of hydrophobic.
C i 0 can be reasonably assumed when the longterm effects are investigated. The combining of sodium chloride and calcium chloride by a number of different hardened cement pastes, cement and concrete research, vol. In order to investigate chloride migration in cracked concrete, considering the. Many researchers have also developed test methods to measure the chloride diffusion coefficient under steady state and non steady state conditions page 1981. The method uses nonlinear chisquare and newtons ncsn method to determine the diffusion coefficient. Ma, nonsteady state chloride diffusion in concrete with different crack densities, materials and structures, vol. A fuzzy control system for reducing urban stormwater runoff by a stormwater storage tank. These models can handle non steadystate conditions and complicated. Solution of ficks second law of diffusion ficks second law of diffusion is given as 265. The present study investigates non steady state chloride diffusion in concrete samples with different crack densities prepared by a non destructive notch method.
However, the proposed model is still helpful for the durability design of uhpc structure in chloride environments. Yang and wang found that there is a linear relationship between the nonsteady state diffusion coefficient obtained from the accelerated chloride. The correlation of chloride diffusion coefficient and concrete maturity value within 56 days of curing was investigated by the chemically combined water content method, rapid chloride migration rcm test, and concrete maturity test. Concentration distribution of chloride ion in cracked concrete. From a physical and mechanical point of view, concrete cracking is hard to avoid. As freeair diffusion coefficients are compound dependent, ranging from 2. Effect of transverse crack on chloride penetration into concrete subjected to dryingwetting cycles. Characteristics of concrete cracks and their influence on. Different physical and chemical transport mechanisms can contribute to chloride ingress, and they depend on the concrete pore structure, micro environmental conditions, temperature, moisture content in concrete, etc. To overcome these drawbacks, nonsteadystate chloride diffusion and migration tests were developed. Based on the experimental and numerical results, a crack influencing factor was determined. Influence of crack depth on chloride transport of cracked.
Electrical migration tests have gained in popularity as a quicker method of measuring transport properties. The different mechanisms of chloride penetration are presented, followed by a further elaboration of the chloride diffusion theory. Chloride ions penetrated into concrete cause rebar corrosion. Modeling the effect of damage on diffusive behavior in a. Following the nt build 492 chloride migration test method, water soluble chloride conetnt, acid soluble chloride content and penetration depth were determined on. Park, kwon, and jung 2012 evaluated the crack effect on chloride diffusion in splitting cylinder concrete by non steady state migration test and proposed an analytical. Nonsteady state chloride diffusion in concrete with different crack densities. Prediction of chloride ion penetration of recycled aggregate. As a corrosion process, rust appears on the surface of a rebar, which induces greater volume of the rebar and cracks of concrete cover 1. The chloride diffusivity for the nonsteady state condition is about 10 times higher than that the steady state condition. In these cases, we can define a fickian diffusivity property d by uid. Bound chloride concentrations water and acid soluble were determined up to 270 days of chloride exposure.
This model is used to derive the corrosion current density and corrosion. A chloride ion is a key factor affecting durability of reinforced concrete rc structures. However, a nonsteady state electrophoretic test, nt bilud 492 of nordtest, has been proposed. However, if the diffusion coefficient is measured after steadystate conditions have. Interest in selfhealing crack technologies for cementbased materials has been growing, but research into such materials remains in the early stage of development and standardized methods for evaluating healing capacity have not yet been established. The results show that the influence of crack depth on chloride concentration of concrete is significant for the concrete zone deeper than 20 mm from the surface. Lattice modeling of chloride diffusion in sound and cracked. Simulation of chloride diffusion in cracked concrete with different. As expected, the discreteness is reduced by taking into account the crack tortuosity, and a linear relationship can be approximately used to relate the chloride diffusivity with the crack density in the concrete. A phasefield approach to fracture coupled with diffusion. Simple technique for tracking chloride penetration in. World academy of science, engineering and technology journals. The correlation of chloride diffusion coefficient and.
Behaviour of concrete under severe environment effect of. Determination of the chloride diffusion coefficient in. In this paper, the boundary condition of cracked concrete and chloride diffusion coefficient in crack were analyzed. Concrete cracks, caused by mechanical loading, thermal stresses, shrinkage etc. Usually, the socalled steadystate diffusion coefficient, ds, refers to the pore solution concentration and therefore expresses the movement of water soluble chlorides. Influence of cracks and crack width on penetration depth of. Time and crack effect on chloride diffusion for concrete. We find a different behavior for small ions in liquid xenon. Lattice modeling of chloride diffusion in sound and. The effect of crack opening size and repair methods on. Kailas mems 10 nonsteadystate diffusion 1 most interesting industrial applications are nonsteadystate diffusion in nature. Applicability of diffuse ultrasound to evaluation of the water. Nonsteadystate diffusion is characterized by ficks second law, which can be expressed as where dcdt is the time rate of change of concentration at a particular position, x.
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